Selective probing of ground state vibrational dynamics in hydrogen-bonded binary mixtures by polarization-sensitive multiplex femtosecond CARS

NRC publication: Ye

Vibrational spectroscopic investigations and density functional theory calculations on trans-diaquabis(picolinato)zinc(II) dihydrate complex

FT-Raman and FT-infrared spectra of pyridine-2-carboxylic acid (picolinic acid) and its corresponding trans-diaquabis(picolinato)zinc(II) dihydrate complex were recorded. Density functional theory was used in order to calculate the optimized geometries and harmonic vibrational wavenumbers of the coordination compound and its isolated ligand. The calculation for the complex was performed under Ci symmetry constraints and all 93 vibrational modes were classified as either Raman active (ag symmetry) or infrared active (au symmetry). The assignment of the characteristic bands was performed by using the calculated harmonic wavenumbers and their Raman intensities. The agreement between the calculated and experimental values of both the structural parameters and the vibrational modes was fairly good. The influence of metal coordination on the picolinic acid was monitored by the wavenumber shift of certain marker bands and the appearance of new vibrational bands

Quantitative determination of contribution by enhanced local electric field, antenna-amplified light scattering, and surface energy transfer to the performance of plasmonic organic solar cells

Plasmonic metal nanostructures are widely used as subwavelength light concentrators to enhance light harvesting of organic solar cells through two photophysical effects, including enhanced local electric field (ELEF) and antenna-amplified light scattering (AALS), while their adverse quenching effect from surface energy transfer (SET) should be suppressed. In this work, a comprehensive study to unambiguously distinguish and quantitatively determine the specific influence and contribution of each effect on the overall performance of organic solar cells incorporated with Ag@SiO2 core-shell nanoparticles (NPs) is presented. By investigating the photon conversion efficiency (PCE) as a function of the SiO2 shell thickness, a strong competition between the ELEF and SET effects in the performance of the devices with the NPs embedded in the active layers is found, leading to a maximum PCE enhancement of 12.4% at the shell thickness of 5 nm. The results give new insights into the fundamental understanding of the photophysical mechanisms responsible for the performance enhancement of plasmonic organic solar cells and provide important guidelines for designing more-efficient plasmonic solar cells in general.Department of Applied Physics201810 bcr

Ultraviolet resonance Raman spectroscopy of anthracene: Experiment and theory

Ultraviolet resonance Raman (UVRR) scattering is a highly sensitive and selective vibrational spectroscopic technique with a broad range of applications from polyaromatic hydrocarbons (PAHs) to biomolecular systems (peptides/proteins and nucleic acids) and catalysts. The interpretation of experimental UVRR spectra is not as straightforward as in purely vibrational Raman scattering (Placzek approximation) due to the involvement of higher lying electronic states and vibronic coupling. This necessitates the comparison with theoretical UVRR spectra computed by electronic structure calculations. Anthracene is an ideal model system for such a comparison between experiment and theory because it is rigid, symmetric, and of moderate size. By taking into account Herzberg\u2013Teller contributions including Duschinsky effects, bulk solvent effects, and anharmonic contributions, a good qualitative agreement close to the resonance condition is achieved. The present study shows that within the framework of time-dependent density functional theory (TD-DFT), a general and robust approach for the analysis and interpretation of resonance Raman spectra of medium- to large-size molecules is available

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

Surface-enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS-based chemical sensors owing to their unique thickness dependent physico-chemical properties with enhanced chemical-based charge-transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future